Inverted urothelial papilloma of the urinary bladder with focal papillary pattern: a previously undescribed feature

Inverted urothelial papilloma: A review of diagnostic pitfalls and clinical management

Inverted urothelial papilloma (IUP) is a rare, non-invasive endophytic lesion that accounts for 1-2% of urothelial tumours. On cystoscopy, IUP appears as a pedunculated/papillary mass with a smooth surface. On microscopy, IUP has an endophytic growth pattern with the bulk of the tumour covered by a superficial layer of urothelium, which can be hyperplastic or attenuated. The cytology should be bland, with uniform, spindled cells arranged in anastomosing trabeculae and cords with peripheral palisading of basaloid cells. Exophytic papillae and mitotic activity should be absent or focal. Pseudoglandular spaces and squamous metaplasia may also be present. There are distinct molecular differences between IUP and urothelial carcinoma (UC). IUP rarely has mutations of FGFR3, homozygous loss of 9p21, or gain of chromosomes 3, 7, and 17, whereas these mutations are frequently seen in UC. In addition, IUP is much less likely to have TERT mutations compared to UC. Immunohistochemistry can also be helpful in distinguishing the two entities as IUP is typically negative for CK20 and has a low Ki-67 proliferation index. Positivity for p53 may be seen in a minority of IUP. IUP can recur and be seen in association with UC. Distinguishing IUP from UC can be difficult due to the similarity between the two entities both on cystoscopy and histology, as up to 25% of UCs will also have inverted growth. Given the morphologic variants of IUP and UC, it is possible for a diagnostic error to occur, which can significantly impact patient management.

The pathology of urinary bladder lesions with an inverted growth pattern

Inverted lesions in the urinary bladder have been the source of some difficulty in urological pathology. The two common ones are von Brunn's nests and cystitis cystic/cystitis glandularis, which are considered normal variants of urothelium. Apart from them, a number of other rare urothelial lesions with inverted growth pattern occur in the urinary bladder. Some of them are only reactive conditions, just as pseudocarcinomatous hyperplasia. Some are benign tumors, namely inverted papilloma. Whereas others are malignant neoplasms, including inverted papillary urothelial neoplasm of low malignant potential (PUNLMP), non-invasive inverted papillary urothelial carcinoma (low-grade and high-grade), and invasive urothelial carcinoma (inverted, nested and big nested variants). Because of the overlapping morphological features of all the inverted lesions mentioned above, even between high-grade invasive carcinoma and pseudocarcinomatous hyperplasia which are only a kind of reactive conditions, it is very important for the surgical pathologist to recognize and be familiar with these inverted lesions in urinary bladder. In this article, we review these spectrums of inverted lesions of the urinary bladder. Emphasis is placed on histogenesis, morphology, differential diagnosis of these lesions, and the pathologic grading of the non-invasive inverted neoplasms, such as inverted papilloma, inverted PUNLMP, non-invasive inverted papillary urothelial carcinoma with low-grade, and non-invasive inverted papillary urothelial carcinoma with high-grade.

A clinical and molecular review of inverted papilloma of the urinary tract: how to handle?

Inverted papilloma (IP) of the urinary tract is classified by the World Health Organisation as a non-invasive urothelial tumour with normal to minimal cytological atypia of the neoplastic cells. During the 1980s, it came under suspicion of having a premalignant or malignant potential and of being concurrent with urothelial cell carcinoma (UCC). This quandary has been proven difficult to solve, due to the fact that IP is very rare and literature mostly consists of case reports with varying levels of information, making strong meta-analyses problematic. New immunohistochemical techniques and genetic approaches are more frequently being used in the attempt to achieve better classifications, prognosis and treatment of lesions hereunder IP. This review will, in our awareness, be the first to combine the knowledge from retrospective studies with these new approaches for determining a possible premalignant potential and concurrency with UCC and subsequently outline a recommendation for follow-up.

MRI Findings of Inverted Urothelial Papilloma of the Bladder

OBJECTIVE

The objective of this study was to characterize MRI findings of inverted urothelial papilloma of the bladder.

MATERIALS AND METHODS

Data pertaining to 16 patients with 18 pathologically proven inverted urothelial papillomas of the bladder who had undergone MRI were retrospectively collected from seven institutions. The shape and surface characteristics of the tumors were evaluated using T2-weighted MR images. In addition, the signal intensity of inverted urothelial papillomas was visually assessed on T1-weighted, T2-weighted, and DW images and on early and delayed phase contrast-enhanced images.

RESULTS

The shape of the 18 inverted urothelial papillomas of the bladder was classified as polypoid with a stalk for 16 tumors (89%) and polypoid without a stalk for two tumors (11%). All stalks were surrounded by urine in the bladder. A total of 15 of the tumor surfaces (83%) were nonpapillary and three (17%) were papillary. All 12 of the inverted urothelial papillomas for which evaluable T1-weighted images were available were isointense with the bladder wall. The lesions had a slightly higher signal intensity than the bladder wall in 15 of the patients (83%) and showed isointensity with the bladder wall in three patients (17%). A total of three patients (17%) had tiny hyperintense foci noted on T2-weighted images. All 16 of the inverted urothelial papillomas examined by DWI had very high signal intensity. All 13 of the lesions for which early phase images were obtained using dynamic contrast-enhanced MRI showed strong enhancement. When compared with early phase images, delayed phase images of the same 13 lesions showed that enhancement was stronger in two lesions (15%), similar in six lesions (46%), and weaker in five lesions (38%).

CONCLUSION

On MRI, the typical appearance of inverted urothelial papillomas of the bladder is a polypoid shape with a nonpapillary surface and a thin short stalk surrounded by urine. Cystic foci are also occasionally seen within the tumor.

Long term outcome of primary urothelial papilloma: a single institution cohort

The aim of this study was to investigate the long term outcome of primary urothelial papilloma (UP). We retrieved 41 primary UP, diagnosed between January 2000 and December 2009. Follow-up was obtained by searching pathology and clinical electronic databases. Mean patient age was 57 years (range 30-84 years), with a male-to-female ratio of 1.9:1. Mean follow-up was 81 months (range 3-127 months). In 37 (90.2%) patients, no recurrence and/or progression were documented and no subsequent higher grade neoplasms were diagnosed. Three male patients were diagnosed with UP at 1, 31, and 43 months after the initial resection; the repeat diagnosis of UP at 1 month likely represented an incomplete resection. Thus, only two of 41 patients (4.9%) had a recurrent UP. One of these patients had a subsequent papillary urothelial neoplasm of low malignant potential (PUNLMP), 17 months after the recurrent UP (48 months after the initial UP). Only one additional male had a subsequent PUNLMP, 76 months after the initial UP. Thus, only two of 41 patients (4.9%) had a subsequent PUNLMP, both presenting with haematuria. Primary UP does not progress to UC when diagnosed using strict criteria, when no previous or concurrent neoplasms are documented, and when complete initial resection is performed.

Long-term clinical outcome of inverted urothelial papilloma including cases with focal papillary pattern: is continuous surveillance necessary?

OBJECTIVE

To investigate the necessity for continuous cystoscopic surveillance of inverted papilloma (IP), including tumors exhibiting mixed morphology (IP with focal papillary architecture).

METHODS

We retrieved all cases of de novo ("primary") IP, diagnosed in our institution during 10 years (from January 2000 to December 2009), from the information database. Patients with a history of urothelial carcinoma or concurrent urothelial carcinoma were excluded. Surveillance was performed by routine cystoscopy, and follow-up was obtained from our institutional and regional clinical and pathology databases.

RESULTS

We identified 35 patients with IP, including 3 with focal papillary architecture. Mean patient age was 60 years (range, 26-88) with male-to-female ratio of 1.9:1. Most common tumor location was urinary bladder (86%), followed by urethra (14%). Focal papillary architecture was identified in 3 patients (aged 51, 52, and 78 years). Mean follow-up was 66 months (median 68; range, 11-132). Only 1 male patient (age 81) had a subsequent diagnosis of IP on follow-up cystoscopy at 9 months; no recurrence or progression was documented in the other patients diagnosed with IP.

CONCLUSION

The absence of progression of IP on long-term follow-up in this study strongly argues against the need of continuous surveillance for patients in whom (1) strict diagnostic criteria are followed, (2) a complete resection can be ascertained, and (3) no previous or concurrent urothelial malignancies are documented. In this study, the 3 patients with IP showing focal papillary architecture had a benign course, similar to the previously documented cases.